Wheatstone-Bridge readout interface for ISFET/REFET applications

The paper presents a novel readout configuration for ISFET sensors based on Wheatstone-Bridge connection. This design technique allows on-chip integration, temperature compensation and measurements from ISFET/REFET pairs. The circuit is capable of operating in differential mode, and can also perform common mode and combined measurements, while improving the immunity to noise and interferences. The Wheatstone-Bridge interface benefits from enhanced operational flexibility, due to the ability of relative sensitivity control of the output signal. Direct and indirect feedback configurations are presented with operational analysis, simulations and application options. Simulation results showing 9 μV accuracy are presented. A 4 mm×4 mm test chip in 1.6 μm CMOS technology was used for laboratory experiments using MOSFETs for emulation of ISFET/REFET sensors.